Improving safety design for machines

Safety design tools help optimize the design process to get machines safety-compliant and operational faster.

George Schuster
Rockwell Automation

When it comes to specifying and designing machine safety systems, manufacturers and machine builders face a long list of challenges. They’re responsible for conducting risk assessments, determining which safety devices to use and which standards to follow, verifying the safety system design, and developing a bill of materials. All the while, the competitive, time-to-market clock is ticking and safety compliance demands are evolving.

It’s not surprising many machine builders can be confused about how to design machines with the appropriate safety technologies that achieve compliance while optimizing the design process.

Fortunately, today there are technologies and tools available to help machine builders optimize safety system designs, more easily meet manufacturer and regulatory requirements for safety and compliance, and save time in the process.

However, no matter which technologies or tools machine builders use, they should first be sure to follow the functional safety life cycle as defined in standards such as IEC 61508, IEC 62061 and ISO 13849. This life cycle helps guide engineers to implement safety into a machine in the earliest stages of the design process, rather than recycling past safety designs or adding safety onto a machine after the design is already set.

Functional safety life cycle design has five steps:

• Perform a hazard or risk assessment – Identify hazards and estimate the associated risk

• Determine the functional safety system requirements – Evaluate safeguarding options based on industry acceptable solutions and select mitigation techniques

• Design and verify the system – Design the system architecture, document safety circuit design and procure materials

• Install and validate the system – Verify systems are operating within defined parameters and applicable standards have been satisfied

• Maintain and improve the system – Verify that system requirements operate within specified parameters for production, safety preventative maintenance and system upgrades

Following these steps leads to improved compliance and identifies opportunities to improve machine productivity. However, the actual design process can still appear complicated and intimidating. Engineers still have to determine which safeguards mitigate certain risks and document that their safety system is compliant with appropriate standards. Fortunately, there are tools that simplify safety system design by providing structured and automated methods for the specification, layout and evaluation of a safety system design.

Safety Design Tools
Before safety system design even begins, machine builders can leverage external, pre-engineered design tools, such as the Safety Automation Builder tool from Rockwell Automation, to develop and evaluate safety design concepts, system layouts, specification, architectures, component selection and a bill of materials. These software-based tools help engineers and designers create an overall design concept that meets specified application requirements and identifies any fundamental errors as early as possible.

With such tools, engineers and designers can identify required safety functions, select safety input, output and logic devices, calculate the achieved system Performance Level (PL) to ISO 13849, identify potentially hazardous access points, place hard and movable guarding, and print machinery layout drawings.

To address the compliance realities of today’s global marketplace, design tools such as the Safety Automation Builder tool integrate with the industry verification tool called SISTEMA. Developed by Germany’s IFA organization, SISTEMA automates calculation of the performance level of safety-related parts of a machine’s control system in the context of ISO 13849.

Instead of having to manually calculate and evaluate Safety Functions within ISO 13849, the Safety Automation Builder tool automatically compiles reports that can be fed directly into SISTEMA. This helps machine builders determine if they have achieved the correct level of risk reduction. Combining SISTEMA with the Safety Automation Builder tool can help machine builders reduce design time and help achieve compliance as specified by end users and industry regulations.

During the design concept stage, machine builders must also consider various critical safety functions. Safety systems in most machinery applications share common safety functions, such as emergency stop, interlocked perimeter guarding and point-of-operation guarding.

Because many of these basic safety functions are repeatable and consistent throughout a variety of machines, Rockwell engineers developed a comprehensive document library of reusable safety functions. These safety functions detail safety system designs created using tools similar to Safety Automation Builder and SISTEMA. The documents provide a knowledge base for machine safety design. Each one includes a safety function description, use and implementation guidance, components that comprise the function, verification using SISTEMA, component interconnection, configuration and programming, and a validation plan for testing the proposed system.

The safety functions can act as a reference for specifying and verifying portions of a safety system in detail. Using these documents can save significant time in hardware and software specification, design and testing, thereby increasing the speed, accuracy and efficiency of safety system design.

Contemporary Safety Technologies
In addition to tools that help save time in the design process, contemporary safety technologies also save time during construction, installation and commissioning.

For example, controllers and drives that combine standard and safety applications – known as integrated safety – can help machine builders shorten design cycles and speed up time-to-market. While integrated safety may not yet be cost-effective for smaller machines, it can reduce engineering time for larger, more complex machines.

Integrated safety only requires one programming environment for discrete, process, batch, motion, safety and drive-based systems. This removes the need to write and coordinate programs on multiple controller platforms. In addition, because controllers and drives that are designed with integrated safety are able to communicate over the network, engineers can make safety configuration changes without time-consuming wiring changes. Integrated safety also allows machine builders to re-use modular hardware designs and machine code modules to optimize machines across similar projects and reduce engineering time from weeks to days.

To learn more about Safety Automation Builder, click here.

For more about pre-engineered safety functions for machines, click here.

George Schuster is a TÜV-certified Functional Safety Expert (FSExp) and a Certified Functional Safety Engineer (CFSE) with Rockwell Automation.